Flexible skin that traps radar waves and cloaks objects

Engineers at Iowa State University claim to have developed a flexible, stretchable and tunable ‘meta-skin’ that uses rows of small, liquid-metal devices to cloak an object from radar.

The materials that make up the meta-skin are composites that have properties not found in nature and said to manipulate electromagnetic waves. By stretching and flexing, the meta-skin can be tuned to reduce the reflection of a range of radar frequencies.

"It is believed that the present meta-skin technology will find many applications in electromagnetic frequency tuning, shielding and scattering suppression," the engineers wrote in their paper.

Working together, the engineers hope to prove that electromagnetic waves - perhaps even the shorter wavelengths of visible light - can be suppressed with these technologies.

The team produced rows of split ring resonators embedded inside layers of silicone sheets. The electric resonators are filled with galinstan, a metal alloy that is liquid at room temperature and less toxic than other liquid metals such as mercury.

The resonators are small rings with an outer radius of 2.5mm and a thickness of 0.5mm. They have a 1mm gap, essentially creating a small, curved segment of liquid wire.

The rings create electric inductors and the gaps create electric capacitors. Together they create a resonator that can trap and suppress radar waves at a certain frequency. Stretching the meta-skin changes the size of the liquid metal rings inside and changes the frequency the devices suppress.

Tests showed radar suppression was about 75% in the frequency range of 8 to 10GHz. When objects are wrapped in the meta-skin, the radar waves are said to be suppressed in all incident directions and observation angles.

"This meta-skin technology is different from traditional stealth technologies that often only reduce backscattering," the engineers wrote in their paper.

Professor Jiming Song, of Iowa State's department of electrical and computer engineering, said that one day, the meta-skin could coat the surface of the next generation of stealth aircraft.

Associate professor, Liang Dong, said: "The long-term goal is to shrink the size of these devices. Then hopefully we can do this with higher-frequency electromagnetic waves such as visible or infrared light. "